This invention relates to cold water supply systems, and more particularly to cold water supply systems in which a computer is incorporated into a refrigeration plant and the optimum capacity control of the variable capacity refrigerator operation is directly controlled through the use of the DDC (Direct Digital Control) function.
One typical conventional system of the type the present invention is concerned with is illustrated in FIGS. 1 and 2. In FIG. 1, in order to ensure that a necessary predetermined amount of cold water or brine at a constant predetermined temperature is always maintained in a supply tank 10, the water level in the supply tank 10 is monitored by a level sensor 12 which supplies a level signal to a computer 14. The computer 14, when a decrease of the cold water level is detected by the level signal from the level sensor 12, starts pumps 16, valves 18 and refrigerators 20 in sequence. At this time, the computer 14 determines and controls the number of the refrigerators 20 to be operated according to the cold water level and the cold water level change rate in the supply tank 10. The computer 14 also automatically controls the pumps 16 and the valves 18 correspondingly. A temperature sensor 26 is disposed in the tank 10 and a level sensor 28 is disposed in the tank 24.
FIG. 2 illustrates the operation of the above described conventional supply system in a flow chart. In FIG. 2, it is seen that a function 101 determines if the cold water level within the supply tank 10 is sufficient for the supply of the water to a load (not illustrated). If the water level is sufficiently high, the refrigeration units of the refrigeration system 20 are not started at all as shown in a function 102. If the water level is not sufficiently high, only one refrigerator 20 is started to operate as shown by a function 103, and the computer 14 calculates and determines in advance which of the two cold water supply amounts, from the refrigerator 20 to the supply tank 10 or the cold water discharge amount from the supply tank 10 to the unillustrated load, is larger from the level change rate as shown in a function 104. The level change rate used herein can be obtained based on the signal from the level sensor 12. When it is determined from the above level change rate that the water level in the supply tank 10 is being lowered, a function 105 determines whether or not the refrigeration system 20 should be stopped with the actual water level also taken into consideration. If the water level is being lowered, a function 106 determines whether or not one more refrigerator 20 of the refrigeration system should be started taking the actual water level also into consideration.
Also, the refrigerating capacity of each of the refrigerators 20 can be changed by the automatic vane control function of turbo-refrigerators, and in order to maintain the cold water temperature constant, the computer 14 automatically controls the refrigeration capacity of the refrigerators 20 so that the cold water temperature at the outlet of the refrigerators 20 is kept constant through the use of the difference between the return cold water temperature measured by a temperature measuring sensor 22 for sensing the temperature of the return water received in return water tank 24 and the temperature of the supply cold water in the supply water tank 10 which latter temperature is kept at a constant set value.
Thus, the computer 14 functions to effect the start-stop control of the refrigeration system, i.e., how many of the pumps 16, the valves 18 and the refrigerators 20 are to be started or stopped by the detection of the level, namely the determination of the amount of the supply water by the level detection sensor 12, and the computer 14 also functions to control the refrigerating capacity of the refrigerators 20 that are actuated by the above start-stop control through the use of the temperature of the return cold water from the return water measuring temperature sensor 22.
Since the conventional cold water supply system is constructed as described above, the number of the refrigerators that should be started up is determined according to the amount of the supply cold water, and the refrigeration capacity of the started refrigerator is automatically determined in accordance with the difference between the cold water temperature and the discharge set temperature (set value). Therefore, with the conventional cold water supply system, the refrigerators sometimes must be operated at a low load factor when the difference between the water temperatures is small which results in inefficient operation, and this is further aggravated when a plurality of refrigerators are started and operated in parallel.